Concrete footings distribute structural weight, allowing the soil to carry the load of the structure. Concrete footings are also used to provide a stable, level platform on which the structure is built. Concrete piers may be used as an upright support connecting a footing to a structural post above grade.
In climates susceptible to freezing temperatures, frost causes the ground to expand and move upward. Frost may adhere to concrete piers, moving the concrete piers as the frost moves. Thus, frost can adversely affect footings even if they extend below the frost line. Smooth concrete piers are less susceptible to frost heave. Additionally, concrete piers with a belled-out bottom portion help resist the upward forces from frost heave.
Concrete footings may be poured using footing forms, and the concrete piers may be formed on top of the footing forms. If using conventional footing forms, a wider hole is dug to allow the footing forms to be placed in the bottom of the hole. This wider hole is then backfilled after the pier is formed.
A poured concrete footing may combine the features of a pier and a footing by allowing the poured concrete to spread out at the bottom to form a bell pier. Bell piers have been used to provide footings for decks, for example. By way of example, it is known to provide a bell-shaped footing form at the bottom of the hole, and then provide a rigid construction tube on the bell-shaped footing form. Concrete can then be poured into the concrete tube and footing form at the same time. However, the use of such footing forms require that a wider hole be dug to allow the bell-shaped footing form to be placed in the bottom of the hole, and then backfilled after the bell pier is formed. It is also known to use only a cylindrical rigid construction tube to form a pier. The hole for the pier is dug with a diameter generally corresponding to the pier diameter. The bottom of the hole may be dug wider to provide room for the concrete to flow to form a bell for a bell pier. The tube is elevated off of the bottom of the hole to allow the poured concrete to fill the wider bottom of the hole and thus form the bell pier.